JP6149674B2 - Radiation CT system - Google Patents

Description

  The present invention relates to a radiation CT apparatus for investigating the internal structure of various industrial products and the like and the presence or absence of defects using radiation including X-rays.

  In an industrial radiation CT apparatus, generally, a table on which a subject is mounted is disposed between a radiation source and a radiation detector arranged to face each other, and the table and a pair of the radiation source and the radiation detector are arranged. Is configured to relatively rotate around a rotation axis orthogonal to the radiation optical axis direction (direction connecting the radiation source and the radiation detector).

CT imaging of the subject, that is, collection of radiation projection data of the subject, was set in advance by rotating a table or a radiation source and radiation detector pair around the rotation axis while irradiating the subject with radiation. For each pitch based on the number of views, that is, an angle obtained by dividing 360 ° by the number of views is used as a sampling pitch to capture the output of the radiation detector (see, for example, Patent Document 1).
By increasing the number of views, the spatial resolution of the obtained tomographic image is improved. Note that the projection data in each view is actually obtained by integrating a plurality of frame data captured at minute time intervals, and by increasing the number of integrations (called average number), the projection data The S / N can be improved and the contrast of the obtained tomographic image can be improved. Hereinafter, in this specification, the projection data capturing operation in each view includes such a summing operation of a plurality of frame data, although not particularly specified.

  In a conventional radiation CT system, in order to obtain a high-resolution tomographic image, a large number of views are set before CT imaging, and the entire tomographic image field is reconstructed using all the projection data when constructing the tomographic image. ing. For this reason, in order to obtain a high-resolution tomographic image, it takes a considerable amount of time for reconstruction.

  Here, in a conventional CT apparatus specialized for obtaining a tomographic image for decomposing a layered structure of a layered structure, that is, a tomographic image intersecting the layer surface of the layered structure, the layer surface is parallel to the radiation optical axis when collecting projection data. A tomographic image representing a layer structure image at a high resolution is obtained by making the sampling pitch finer than the other projection angles for a predetermined projection angle range set in advance on both sides of the rotation angle as a reference. Time required for reconstruction by roughening the sampling pitch of the projection angle range that does not contribute to the resolution of the layer structure on the tomographic image, that is, the projection angle range in which the radiation optical axis intersects the layer surface at a large angle Has been proposed (see, for example, Patent Document 2).

JP 2004-219224 A Japanese Patent No. 4598880

  By the way, in a conventional CT apparatus that reconstructs the entire tomographic field uniformly using all projection data collected with the number of views set prior to CT imaging, it takes time to reconstruct to obtain a high-resolution tomographic image. It is as described above that it takes. On the other hand, in order to display an image of the layer structure of the layered structure with high resolution, the conventional proposed technique for finely sampling the sampling pitch only in a predetermined angle range on both sides centered on the projection angle parallel to the layer surface, Since the data collection and the reconstruction calculation are performed with the sampling pitch in the other angle range being rough, the time required for the reconstruction is shortened. However, in this method, it is necessary to set the angle range for reducing the sampling pitch before CT imaging, and not so much when the direction of the layered structure and the appearance of the subject clearly correspond, For a subject in which the direction of the layered structure cannot be visually recognized from the outside, there is a problem that it is difficult to set an angle range for reducing the sampling pitch. In any case, if the angle range set before the CT imaging is deviated from the direction of the actual layered structure of the subject, there is a problem that the CT imaging has to be performed again from the beginning.

  In addition, in any of the conventional methods described above, there is a problem that the number of views cannot be changed after CT imaging.

  The present invention has been made in view of such circumstances, and by specifying an arbitrary projection angle range after CT imaging, the number of views in the specified projection angle range can be increased, and the resolution of the projection angle range can be increased. An object of the present invention is to provide a radiation CT apparatus capable of increasing the image quality.

In order to solve the above problems, the radiation CT apparatus of the invention according to claim 1 is provided with a table on which a subject having a layered structure is mounted between a radiation source and a radiation detector arranged to face each other. A view that is set by irradiating the subject on the table with radiation while rotating the table and the pair of radiation source and radiation detector around a rotation axis that intersects the radiation optical axis. The output of the radiation detector is captured at a pitch based on the number, radiation projection data at a plurality of projection angles of the subject is collected, and reconstruction calculation using the radiation projection data is performed by the reconstruction calculation means, and the rotation axis orthogonal to build a tomographic image of the subject along the slice plane, a radiation CT apparatus for displaying the tomographic image on the display device, based on the view number V1 which is set in advance Captures the radiation projection data with a small pitch, designation for designating a photographing operation control means to continue to store the projection data memory means that each of the radiation projection data captured, the projection angle Dohan circumference and number of views V2 and (V2 ≦ V1) And the reconstruction calculation means collects projection data based on the number of views V1, and then performs reconstruction calculation based on a small number of views V3 (V3 <V2) in which the entire projection angle range is set in advance. The rough overview tomogram is constructed to display the overview tomogram on the display, and the designation means displays the overview tomogram along the layered structure of the subject on the display. configured to perform the specified the projection angle range as the angle range around the straight cursor, further the reconstruction operation unit, the projection angle range specified by the specifying means, The projection data corresponding to the specified number of views V2 by said designating means, for the projection angle range except for the designated projection angle range, the projection data corresponding to the view number V3, each of the projection data storage means It is characterized by extracting from the stored contents and subjecting it to a reconstruction operation to construct a tomographic image.

The present invention stores a large number of views at all projection angles at the time of CT imaging, that is, stores radiation projection data collected at a fine pitch, and specifies each projection angle range after collecting the data, thereby collecting each collected radiation projection data. Used appropriately and appropriately during the reconstruction calculation.

Ie, projection data corresponding to the specified number only specified projection angle range view, also by performing a reconstruction operation by using the projection data of the coarse sampling pitches in the projection angle range of otherwise A fine tomographic image is to be obtained only in the designated projection angle range.

  That is, at the time of CT imaging, radiation projection data is collected with a preset number of views V1. By setting the value of the number of views V1 large, radiation projection data is collected at a fine angle pitch. And memorize it.

  Before performing reconstruction calculation using the radiation projection data acquired as described above and stored in the projection data storage means, an arbitrary projection angle range is specified, and the view number V2 (V2 ≦ V1) is also specified. To do. The reconstruction calculation means employs projection data corresponding to the designated view number V2 for the designated projection angle range, but is set in advance for projection angles other than the designated projection angle range. Projection data corresponding to a small number of views V3 (V3 <V2) is adopted, and reconstruction calculation is performed using those projection data. Thus, for example, by designating a predetermined angle range on both sides of the projection angle range along the layered structure, it is possible to construct a tomographic image in which only the specified angle range is fine and the others are rough. While refining the tomographic image of the layered structure, the reconstruction operation time as a whole can be shortened. In the present invention, the projection angle range for constructing the tomographic image by making the sampling pitch fine can be designated at any time after CT imaging. Therefore, the angle range is set in advance as in the technique of Patent Document 2 described above. There is no need to designate, and there is no need to redo CT imaging even when the designated angle range is deviated.

Here, the specified method of the projection angular range, after C T photographing, rough tomographic image, that is to construct an overview tomographic image to the extent that the internal structure of the object is known, by specifying in its overview tomographic image, for example, It is possible to accurately specify a projection angle range that requires fine reconstruction calculation after determining the direction of the layered structure.

According to the present invention, after collecting and storing projection data at a fine sampling pitch, by designating the projection angle range, the projection data corresponding to the designated number of views is also obtained for the designated projection angle range. For example, the projection angle range other than that is extracted from the stored one, and projection data corresponding to a small number of views set in advance is extracted and used for each reconstruction operation. For a subject, projection angle data that does not contribute to the resolution of the layered structure can be displayed in a tomographic view with high resolution while reducing the number of views and shortening the time required for the reconstruction calculation. It becomes possible. Moreover, since the projection angle range in which the reconstruction calculation is performed with the number of views increased can be performed as needed after CT imaging, even when the designated projection angle range is deviated from the direction of the layered structure, Thus, it is possible to change the designated projection angle range without starting CT imaging from the beginning.
In addition , on the rough tomographic image reconstructed after CT imaging, for example, while confirming the direction of the layered structure, the projection angle range to be subjected to fine reconstruction operation is specified, thereby improving convenience. Can do.

The figure which shows together the schematic diagram showing the mechanical structure of embodiment of this invention, and the block diagram showing a functional structure. The flowchart which shows the operation | movement of reconstruction calculation from CT imaging | photography of embodiment of this invention. It is explanatory drawing of the setting method of the projection angle range in embodiment of this invention, Comprising: (a) is explanatory drawing at the time of designating the center of projection angle range on an overview tomogram, (b) is a view by the designation | designated Explanatory drawing of the projection angle range using several V2 projection data.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing a schematic diagram showing a mechanical configuration of the present invention and a block diagram showing a functional configuration.

  The radiation source 1 is arranged so as to generate cone-beam-like radiation in the horizontal direction (x-axis direction), and a two-dimensional radiation detector 2 is arranged opposite to the radiation source 1. A turntable 3 is provided. The radiation source 1 is, for example, an X-ray generator using an X-ray tube. The radiation detector 2 is, for example, a flat panel type X-ray detector.

  The turntable 3 is rotated about a rotation axis R along a vertical direction (z-axis direction) orthogonal to the X-ray optical axis direction along the x-axis direction connecting the radiation source 1 and the radiation detector 2. . The rotary table 3 can be moved in the radiation optical axis direction (x-axis direction) by driving a moving mechanism (not shown), and the magnification of CT imaging is determined according to the position in the x-axis direction. The direction of the radiation optical axis and the direction of the rotation center axis do not necessarily have to be orthogonal, and may be arranged to intersect at an angle that is not orthogonal. That is, the present invention can be applied to an inclined radiation CT apparatus.

  At the time of CT imaging, the rotation table 3 is rotated while irradiating the radiation from the radiation source 1 with the subject W mounted on the rotation table 3, and the output of the radiation detector 2 is output at every predetermined minute rotation angle. The image data is fetched into the image data fetch circuit 11. The information output from the radiation detector 2 is a radiation transmission image of the subject W, and the frame data is stored in the projection data storage unit 12 as radiation projection data. The storage method is selected CT imaging. It depends on the mode. This point will be described later.

  The radiation projection data stored in the projection data storage unit 12 is subjected to a reconstruction calculation by the reconstruction calculation unit 13, and the method of the reconstruction calculation also differs depending on the selected CT imaging mode. . This point will also be described later.

  The tomographic image reconstructed by the reconstruction calculating unit 13 is stored in the tomographic image storage unit 14. The tomographic image stored in the tomographic image storage unit 14 is displayed on the display unit 17 as designated by the display control unit 16 according to a command from the operation unit 15. The operation unit 15 includes a mouse, a keyboard, a joystick, and the like. The operation unit 15 can be used to select the mode and set the number of views, and can move the rotary table 3 in the x-axis direction. You can also change the shooting magnification.

  The rotation of the image data capturing circuit 11, the projection data storage unit 12, the reconstruction calculation unit 13, the tomographic image storage unit 14, the display control unit 16, and the rotary table 3 is placed under the control of the control unit 18. The control unit 18 controls the CT imaging operation based on the mode selected by the operation unit 15 and the designated number of views, and also performs various calculations by the reconstruction calculation unit 13 according to the specification by the operation unit 15. Control its operation.

  In the present invention, the normal mode and the specified angle range fine reconstruction mode can be selected as the CT imaging mode. The operation in each mode from CT imaging to reconstruction calculation will be described below with reference to the flowchart of FIG.

  First, in the normal mode, projection data corresponding to the sampling pitch corresponding to the set number of views is collected. Therefore, when data collection is completed, the same number of projection data as the number of views is stored in the projection data storage unit 12 shown in FIG. The reconstruction calculation unit 13 constructs a tomographic image with uniform resolution and contrast over the entire tomographic image visual field by back projection using all projection data stored in the projection data storage unit 12.

  Next, when the designated angle range fine reconstruction mode is selected, projection data is collected and stored in the projection data storage unit 12 based on the number of views V1 set arbitrarily or set exclusively for this mode. To do. The view number V1 value in this CT imaging is a large value. That is, projection data is collected at a fine angle pitch.

  The tomographic image initially constructed in the designated angle range fine reconstruction mode is a rough tomographic image obtained by reconstruction using only a part of the projection data stored in the projection data storage unit 12 as described above. That is, an overview tomographic image. Specifically, the projection data is collected by the number of views V1 per one rotation of the rotary table 3, but only a fraction of the projection data is used in a thinning manner and used for the reconstruction calculation. . That is, the view number V3 of the projection data used for the calculation of the overview tomographic image is considerably smaller than the view number V1 at the time of data collection.

  The overview tomographic image thus constructed is incorporated into a GUI display for designating a projection angle range and displayed on the display unit 17. On the overview tomographic image, the operator designates a projection angle range in which a high-resolution tomographic image is obtained by performing a fine reconstruction operation and a view number V2 used for the reconstruction operation of the projection angle range. The view number V2 is basically the same as the view number V1 at the time of data collection, but may be arbitrarily specified within the range of V1. A method for setting a projection angle range to be subjected to fine reconstruction calculation in the present invention will be described with reference to FIG. FIG. 3A is an explanatory diagram when designating the center of the projection angle range on the above-described overview tomographic image, and FIG. 3B is an explanatory diagram of the projection angle range using the projection data of the view number V2 by the designation. It is.

  As shown in FIG. 3A, on the general tomographic image P of the subject appearing in the tomographic image field Q, for example, a linear cursor C is set along the direction of the layered structure of the subject, thereby providing a projection angle range. Specifies the center angle of. That is, the overview tomographic image P is displayed based on the posture of the subject at the start of CT imaging, and when the initial projection data collection angle is 0 °, the angle becomes a horizontal line on the display as shown in the figure. It becomes an angle along. The angle range in which the reconstruction operation is to be finely performed in the subject having the layered structure is an angle range before and after the direction along the layered structure, and by moving the linear cursor C along the layered structure, The center angle θ can be specified. The angle range is specified in the form of ± φ, for example, by operating the operation unit 15. With the above specification, the projection angle range to be subjected to fine reconstruction calculation is designated as θ ± φ among the projection angles 0 ° to 360 °.

  That is, by specifying the above projection angle range, the projection angle range in which the reconstruction calculation is performed based on the view number V2 in FIG. 3B is centered on the angle advanced by θ with respect to the projection angle 0 °. This means that the projection angle range from θ−φ to θ + φ is designated. Summarizing the relationship between the numbers of views in the above embodiment, the relationship between the sizes of V1, V2, and V3 is V3 <V2 ≦ V1.

  The reconstruction calculation unit 13 reads out necessary data from the projection data storage unit 12 and reconstructs the projection data in the designated projection angle range θ ± φ using the specified view number V2. Use for construction. As projection data other than the designated projection angle range θ ± φ, the projection data used for the overview tomogram constructed previously, that is, the projection data of the view number V3 can be used as it is.

  According to the above embodiment, since the reconstruction calculation is performed with a small number of views as projection data of angles other than the designated projection angle range θ ± φ, the fine projection data is achieved while shortening the entire reconstruction time. Is calculated with a large number of views, and a high-resolution tomographic image is displayed. In addition, the projection angle range θ ± φ can be arbitrarily specified by the operator while viewing the overview tomographic image, so that the internal structure does not correspond to the external appearance of the object, or the internal structure. Even if the subject is unknown, it is possible to accurately set the projection angle range that requires fine projection data.

  Note that by designating the projection angle range θ ± φ, reconstruction may be performed based only on the angle range of θ ± φ based on the view number V2, but the projection angle on the back side, that is, FIG. With respect to the projection angle range of θ + 180 ° ± φ indicated by the broken line, the reconstruction calculation may be automatically performed based on the view number V2 by the above designation.

  In the above embodiment, an example in which the table on which the subject is mounted is used as a rotary table and rotated with respect to the pair of the radiation source and the radiation detector is shown. However, the table is fixed without rotating, and the radiation source Of course, the present invention can be equally applied to a CT apparatus having a structure in which a pair of radiation detectors is rotated around a table.

DESCRIPTION OF SYMBOLS 1 Radiation source 2 Radiation detector 3 Rotation table 11 Image data acquisition circuit 12 Projection data storage part 13 Reconstruction calculation part 14 Tomographic image storage part 15 Operation part 16 Display control part 17 Display 18 Control part R Rotating axis W Subject Q Tomographic field of view P Overview Tomographic image

Claims (1)

A table for mounting an object having a layered structure is provided between a radiation source and a radiation detector arranged opposite to each other, and the table and the pair of the radiation source and the radiation detector intersect a radiation optical axis. A plurality of projections of the subject are obtained by irradiating the subject on the table while irradiating the subject around the rotation axis and capturing the output of the radiation detector at a pitch based on the set number of views. collect radiation projection data at an angle, to construct a tomographic image of the subject along the slice plane orthogonal to the rotation axis performs reconstruction operation using the radiation projection data by the reconstruction operation unit, the tomographic image In a radiation CT apparatus that displays
An imaging operation control unit that captures radiation projection data at a minute pitch based on a preset number of views V1, and stores the captured radiation projection data in a projection data storage unit;
Comprising a specifying means for specifying the projection angle Dohan circumference and number of views V2 (V2 ≦ V1),
The reconstruction calculation means collects projection data based on the number of views V1, and then performs reconstruction calculation based on a small number of views V3 (V3 <V2) in which the entire projection angle range is set in advance. Build an overview tomogram and display the overview tomogram on the display.
The designation means is configured to designate the projection angle range as an angular range before and after a linear cursor displayed on the display along the layered structure of the subject together with the overview tomographic image,
Further, the reconstruction calculation means, for the projection angle range designated by the designation means, converts projection data corresponding to the view number V2 designated by the designation means to projection angles excluding the designated projection angle range. the range, the radiation CT apparatus characterized by constructing a tomographic image projection data corresponding to the view number V3, respectively and subjected to extraction to reconstruction calculation from stored contents of the projection data storage unit.

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